There are various types of bags on the market and in the technical literature with reclosable fastener strips. These bags are made from a variety of materials and assume a variety of forms, reflecting such factors as whether or not the bags are supplied to consumers with a product inside, what type of material they are designed to hold, and the direction and orientation by which they are to be opened. The materials include cellophane, plastics such as polypropylene and mylar, and foils such as tin and aluminum foils, including those with a laminated plastic or cellophane backing. The fastener strips are of mated resilient material permitting opening and closing by hand to form a mechanical closure which can be made air-tight and water-tight. A typical bag generally has an axial direction defined during its manufacture as perpendicular to the transverse end seals which close off the cylindrical plastic web material from which the bag is formed. Manufacturing procedures vary from those in which the reclosable fastener strip is placed longitudinally (parallel to the bag axis) to those in which the strip is placed in a direction transverse to the bag axis.
The reclosable bags addressed by this invention are those in which the reclosable fastener strip is transverse to the bag axis. One example of such a bag is one which when supplied to the consumer has top and bottom ends fused together with a product hermetically sealed inside, the reclosable fastener strip forming a auxiliary closure toward the top end for repeated closing and reopening after the fused closure has been broken, each time producing an air-tight seal. This combination of closures protects the user against tampering with the bag and contents with between bagging plant and point of purchase, while affording the user the option of tightly reclosing the bag after removing only a portion of the bag's contents after the initial opening. Information relevant to the construction and manufacture of such bags is found in Christoff, P.B., U.S. Pat. No. 4,617,683, issued Oct. 14, 1986, and other patents cited therein.
A method typically used in the industry for forming plastic bags is that disclosed in the Christoff patent. A continuous sheet or web of the plastic material is drawn over and wrapped around a forming tube by drawing the two edges of the sheet together to form a seam or fin parallel to the tube axis, the seam being fused while still on the tube by vertical heat sealing bars positioned along on the tube exterior. Product is fed to the tube interior through a hopper at the top, above the level at which the plastic web first contacts the tube. At a point below the lower extremity of the forming tube, the bag material, now in cylindrical form, is sealed off in the transverse direction by horizontal heat sealing bars, thereby forming seals commonly referred to as jaw seals, and severed to form separated bags, each sealed shut at both top and bottom ends with a measured quantity of product inside. Advancement of the web may be performed in various ways. One example is by the jaw seal bars which move downward in increments while still gripping the jaw seals. Another example is by drive belts on the side of the forming tube, gripping the material by friction or by vacuum. In either case, the downward movement coordinated with the incremental feed of product to the hopper and the activation of the fin seal bars.
Attachment of the reclosable fastener strip on the web material is performed in the Christoff disclosure at a point in the web path upstream of the first contact of the web with the forming tube. A single continuous strip of extruded plastic material is drawn across the width of the web and, once in position, cut to the length of the web and bonded to it. The web is then wrapped around the forming tube, its edges joined and fused to form the fin seal, and the web in cylindrical form is then flattened to form the jaw seals as described above. During this process, the strip of extruded plastic material is folded over itself, its two facing surfaces having been contoured to mate in a manner permitting them to become engaged and disengaged by manual pressure to form the reclosable closure.
One concern raised by such a process is the need for precise alignment of the two halves of the folded fastener strip material when it reaches the jaw seal bars. Deviations from proper alignment will preclude an effective mating of the two halves of the strip material, rendering the strip useless. Such deviations will result from skewing, stretching or other distortion of the web at any point in the travel path of the web both on its approach to and its passage over the forming tube. Since there is a considerable distance between the points in the web path where the fastener strip is bonded to the web and where the web is closed to form the jaw seals, any deviations or readjustments occurring along this portion of the path will cause such a misalignment.
Another concern is the complicated mechanism and succession of motions involved in drawing the fastener strip material across the spread web. A carrier first travels the full width of the web to position the strip material, then travels the same distance in the opposite direction to regain its original position and prepare for a new length of the strip material. These are time-consuming steps in an otherwise continuously repeated process.
A still further concern is the requirement for fastener strip material which must mate and interlock with itself when folded over. The contacting faces being of identical contour are capable of interlocking only when offset. Thus, even when the two halves are perfectly aligned, the bag will never be perfectly flat when closed and the reclosable closure never perfectly aligned.